Process and device for producing thin walled or extra-thin walled smooth tubes by welding

ABSTRACT

A process and apparatus for thin-walled tubes from strips having a thickness of 0.03 - 0.7 mm, for example, wherein the tube blank formed by curving the strip is continuously moved past a stationary electrode to weld the same.

United States Patent Doublet Aug. 7, 1973 PROCESS AND DEVICE FORPRODUCING THIN WALLED OR EXTRA-THIN WALLED SMOOTH TUBES BY WELDINGinventor:

Leu, France Societe Anonyme Tubest, Paris, France Filed: June 9, 1971Appl. No.: 151,317

Assignee:

Foreign Application Priority Data Field of Search ..219/59-67, 158, 160,161, 8.5, 105; 228/5; 29/482 Fernand Noel Doublet, La Croix St.

[56] References Cited UNITED STATES PATENTS 3,075,484 l/1963 v Benteler228/17 X 2,306,945 12/1942 Hebron..... 219/105 X 2,716,691 8/1955 Bowman219/60 R 2,654,014 9/1963 Schaefer 219/60 R Primary Examinerl. V. TruheAssistant Examiner-L. A. Schutzman Att0rneyGreene & Durr [57] ABSTRACT Aprocess and apparatus for thin-walled tubes from strips having athickness of 0.03 0.7 mm, for example, wherein the tube blank formed bycurving the strip is continuously moved past a stationary electrode toweld the same.

13 Claims, 8 Drawing Figures I a l P l I 1." O O 2 a O Q 3 I O l 32 2/ II I 1 1 k w J p i j .,4

A B C D E Pmmau W5 INVENTOR. 1-. N. Baum-Er BY q 2 ATTORNEY PATENTEM3,751,623

SHEEI 2 OF 5 fla IN VEN TOR. FNDOUBLET ATTORNEY PAIENTEUMJQ 11m3.751.623

SHEET 5 OF 5 '0 m INVENTOR.

FIVDOUBZET ATTORNEY PROCESS AND DEVICE FOR PRODUCING THIN WALLED OREXTRA-THIN WALLED SMOOTH TUBES BY WELDING CROSS REFERENCE TO RELATEDAPPLICATION Applicants prior application, Ser. No. 878,279, filed Nov.20, 1969, now US. Pat. No. 3,610,863, issued on Oct. 5, 1971, entitledAPPARATUS FOR THE PRO- DUCTION OF THIN METAL TUBES discloses a similarprocess and apparatus except that in said prior application, the weldingelectrode is moved longitudinally along the tube blank. Such tubes aredisclosed to be high quality tubes suitable in particular for processinginto corrugated pipes, for example, by hydroforming.

This invention relates to improvements thereto, providing on the onehand, for a substantial simplification of the device, and on the otherhand, for a substantial increase in production.

Essentially, the process, according to the invention'is characterized inthat, while using practically the same tube blank conformation andwelding means as in the previously mentioned application, the productionis carried out as a continuous operation, whereas, according to saidapplication, operations were carried out in successive steps. Thetechnical progress achieved is very significant. .Indeed, all idle timesinvolving the return of the welding torch to the starting position, andthe tighteningand loosening of the jaws seizing the tube blank,indisconnecting the arc, and in the opening and closing controls forprotective gas pipes, which are to be effected at each advance step, arethus eliminated. Thetorch remains stationary andthe tube blank goes byin front of it, at a constant speed, until the strip of sheet metal,which provides this tube blank, is used up. Asthe ends of rolls of sheetmetal for the tube blank can be joined together, the length of the tubeproduced can be practically unlimited.

The characteristics of the invention will best appear from thedescription which will now be given of an embodiment shown simply by wayof illustration in the appended drawings, in which: L

FIG. 1 is an overall elevation and partial vertical longitudinalcross-sectional view of the machine;

FIG. 2 is a cross-sectional view to a larger scale, approximatelyalongplane II-II of FIG.'1;

III-III of that same figure; M I

FIG. 4 shows the main components of this machine, partly in perspectiveand partly as a vertical longitudinal section; i

' FIG. 5 is a partial view showing avertical longitudinal section of analternative embodiment of the invention;

FIG. 6 is a partial vertical longitudinal sectional view to a largerscale;

- FIG. 7 is a sectional view, approximately along plane VII-VII of FIGS.1 and 6, and

FIG. 8 is a view similar to that of FIG. 4, showing a varyingembodiment.

The machine, according to the invention, comprises the following maincomponents, listed in the order in which they go into operation.

a series of vertical forming rollerpairs in an appropriate number,designated as A in FIG. 1, processing in a known manner a strip of sheetmetal 1 provided by a feeding coil, not shown, first as a gutter FIG. 3.is anothersection, approximately along plane 2 and then as a tube blank3 open along its upper generatrix.

a pair of horizontal rollers designated as B, completing theconformation of the tube blank;

a die-conformator unit, designated as C;

a welding unit, designated as D, and which comprises essentially,according to the invention, and in addition to the known welding torch4, two external half-shells and an internal support-distributor;

finally, a pair E of horizontal rollers designed to guide the weldedtube which, as it exits from the machine, is seized and propelledcontinuously by a pair of caterpillars of known construction, not shown.

The pairs of forming rollers, considered individually, are notsubstantially different from those already described in the previouslymentioned application, but, according to the invention, each pair isarranged at a level which is slightly higher than that of the precedingpair, in the direction of feed of the strip of sheet metal, so that theedges of the blank are subjected to a tensile stress. Applicant hasindeed noted that, when forming the tube blank, its lower part travels,during its movement up to the die, over a shorter distance than-itsedges, thus leading to the formation of folds. This drawback iseliminated very simply by the arrangement adopted. The optimum slope tobe given to the tube blank is determined by the relative location of thesuccessive pairs of rollers which, to this effect, are verticallyadjustable in their supporting cages, which are in turn horizontallyadjustable with respect to'one another.

The horizontal rollers B do not, by themselves, have any originalcharacteristic. However, it should be mentioned that each of them isadjustable in the horizontal plane with great accuracy, through use ofan appropriate micrometer screw device. It is indeed important that thetwo lips of the tube blank maintain between them the free passage of theend part of the supportdistributor which will be described later,without being damaged in any way by the same.

The tube blank thus prepared then moves into the die conformator unitdesignated as a whole as C, which acts in a manner already described inthe previous application, so as form thereon, on each edge, a joininglip 5 (see FIG. 7). However, and according to the invention, theconformation of the tube blank before welding can be providedforaccording to two different methods, to which correspond respectivelyFIGS. 2, 4 and5,8. J 1

According to the first of these, die 10 is constructed in two parts,separated along a horizontal plane including the diameter. In a knownmanner, forming plates ll made of treated metal reinforce the edges ofthe upper slit of the die, which is itself made of a material having avery low friction coefficient, and whose section continuously decreasesbetween the inlet end and the outlet end of the latter, to actprogressively on the tube blank and apply its edges on the conforming orlip forming boot 12 known from the previous application. The latter ishinged to a support 13, adjustable particularly in the verticaldirection with great precision, by means of a micrometer screw.

In this first embodiment shown in FIGS. 2,4, the two parts of the diehave their end faces in coincidence, as shown in FIG. 4, and theconforming boot 12 is housed and supported in the upper part of saiddie. It must indeed be perfectly maintained and guided, considering thehigh stresses to which it is subjected upon formation of the lips 5.

In the second embodiment of the machine, shown in FIGS. 5 and 8, lips 5,instead of being completely obtained through cooperation of the die andthe conforming boot 12, as mentioned above, are preformed by the rollersof unit A. Thus the conforming boot 12 now provides only for thecompletion of the lips, and it can therefore be positioned downstream ofdie 10, at a location where it will be completely unconstrained. I

A disk 15 is fixed, at the outlet end of die 10, to a mounting 16 whichis itself assembled to support 17 of the die, this disk forming, inorder to correctly guide and maintain the tube blank 3 upon its entranceinto welding unit D, a central circular opening whose diameter ispractically equal to the external diameter of the tube blank, with anotch providing for the passage of the lips 5. It acts furthermore, as ashielding screen to prevent overheating of die 10 by the welding are.

In the second embodiment, the die consists of two parts, 13a, 13bseparated along a median horizontal plane (see FIGS. 5 and 8), its upperpart 13a being shifted towards the upstream side of said die, togetherwith the conforming boot 12 associated with it, thus moving them awayfrom the electric arc of torch 4.

The tube blank thus conformed then passes into the welding unit itself,designated as D in FIG. 1. As shown in FlG. 7, it consists essentiallyof two half-shells 20a, 20b and of a support-distributor 21, betweenwhich the tube blank moves in a continuous motion, according to theinvention. Half shells 20a, 20b are mounted in sliding supports 22a,22b, which, through their transverse displacement controlled by anysuitable means, not shown, provide for the accurate adjustment of thesetwo half-shells with respect to the support-distributor.

According to another characteristic of the invention, half-shells 20a,20b freely oscillate around horizontal pivotal axis 23a, 23b, thusproviding for their selforientation with respect to the tube blank 3,and thus facilitating its passage. Said sheels 20a, 20b are providedwith bores or channels 24 in appropriate number and arrangement, for thecirculation of a gaseous or liquid' refrigerating fluid, so as to removea substantial part of the heat given off during the welding operation.For the same purpose, -supports 22a, 22b are provided with cooling finsor blades 25, which also provide for thermal dissipation. Inlet andoutlet tubings for the re- 'frigerating fluid, not shown, are connectedto the correspondinghalf-shells channels, designated by 24a, 24b in FIG.4. J i

Furthermore, a small horizontal plate 28 of treated steel comprising agroove 29 on its lower face (see FIG. 7), in which the two lips 5 of thetube blank 3 are engaged, is provided upstream of the welding torch 4,but in the direct vicinity of the latter; said plate being pressedagainst the upper face of half-shells 20a, 20b, by means of jaws 30which are tightened by screws as shown in FIGS. 6 and 7. The plate 28can also be provided in two parts which are contacting in the verticalwelding plane. I

Experience has shown that the surface condition of the half-shells 20a,20b between which the tube blank passes, plays an important role inpractice. They must be ground and polished with great care, so as toavoid gripping of the tube blank and contamination of the weld byparticles of the metal of which these half-shells are made. They mustalso be made of a material which will eliminate any instability of theelectric are by magnetic blow out.

According to the invention, an elastic or resilient assembly ofhalf-shells can also be provided, so that they can absorb expansions dueto heating, while maintaining an accurate pressure contact on the lipsof the blank. To this effect, and as shown in FIG. 3, the halfshells aremaintained close to each other by compression springs 31 surroundingaxles 23a, 23b and bearing, on the one hand, against supports 22 and, onthe other hand, against said half-shells.

As already mentioned above, the tube blank is accurately guided, at thetime of welding, by means of halfshells 20a, 20b and support-distributor20, whose roles is very important, and which will now be described ingreater detail, referring more particularly to FIG. 6. It is essentiallyintended to protect the inner side of the weld against oxydation byadequately localizing the protective gas, to prevent the collapse of themelted metal bath so as to ensure a smooth appearance of the weld, andalso to contribute to thermal dissipation.

According to the invention, said support-distributor comprises a tubularbody 21 fixes to the downstream end of a retaining tube 32 coaxial withthe latter and which carries, in the vicinity of its upstream end, anend piece 33 (see FIG. 4 or 8) directed vertically upwards, passingbetween both edges of the tube blank 3. The length of tube 32 is chosenso that endpiece 33 will be located in a zone in which-these edges willbe sufficiently far apart from each other so as not to risk any damagefrom the latter. This end piece is hinged to a fork 34 supported by asupporting rod 35 whose opposite end is attached to the frame of themachine in any appropriate manner. It is thus possible, by moving fork34 on rod 35, to accurately adjust the longitudinal position of thesupport-distributor 21 with respect to torch 4. Moreover, the end piece33 can freely oscillate around its axis of attachment to fork 34, so asto provide for the self-alignment of support-distributor 21 in side thetube blank.

Just like half-shells 20a, 20b, support-distributor 21 is bored withchannels, not shown, designed for circulation of a refrigerating fluidwhich arrives therein through an inlet tubing 26 and is evacuatedthrough an outlet tubing 27, as shown in FIG. 4.

According to the inventionfietaining tube 32 is also used to feedsupport-distributor 21 with protective gas. To this end, it is connectedthrough its upstream end to an inlet tubing 36 which, just like lines 26and 27, pass through the upper slit of the tube blank3.

Radial channels such as 38 (FIG. 6) communicate with the blind centralbore 37 of support-distributor 21, said radial channels conducting theprotective gas in a median longitudinal upper groove 39 corresponding tothe weld seam.

It is very important practically to provide for a constant flow and gooddistribution of the protective gas, and this condition is satisfied,according to the invention, by suitably choosing not only the number andlocation of channels 38, but also the profile of groove 39, which is ofa general trapezoidal section, and whose depth and width vary along itslength, as a function, in particular, of the characteristics of themetal of which the tube blank 3 is made, and of the welding processadopted (for example TIG or Micro-plasma).

Just as half-she1ls a, 20b, the support-distributor 21 must also have anappropriate surface condition. For example, it will be chromed orpolished, so as to avoid gripping and especially entrainment ofparticles of metal which would risk contaminating theweld.

Further, and according to the invention, said support-distributor hasadditional features, each of which contributes to the high .quality ofthe weld obtained.

First of all, it comprises two diametrically opposed lateral flatsurfaces 40, v40', (see FIG. 7) which reduce the friction of the tubeblank, upon its passage against the same. Its external diameter- D.overa certain length L (see FIG. 6), is very slightly greater than theinternal diameter of the tube blank to be welded. Over another lengthLl, its external diameter (1 becomes smaller than the internal diameterof the tube blank. Over a third length L2, its external diameter dl isstill further reduced to a greater extent. Finally, over the last lengthL3, its external diameter d2 becomes equal again to di-v ameter D.Channels 38 open into zones L and Li, and the zone Ll being that inwhich the welding is carried out. The size of channel 38a opening intothis zone, straight beneath the welding torch 4, isgreater than that ofthe other channels 38. The outlet opening of this channel 38a is ataminimaldistance L4 from the rear edge of small plate 28, so as to avoidthe initiation of an are on the latter; however, the welding point issufficiently close to this smallplate to prevent any deformation of themetal through aithermal effect over this length L4, and thus providesfor a good interfusion of the two lips 5. I

As far as zone L2 is concerned, it forms an annular peripheral chamberin which the protective gas is retained, so as to provide both adeoxidizing and cooling action. Zone. L3 partially closes the previouslymentioned chamber, while providing for the. measured evacuationof partof the hot protective gas. The channels for the circulation of therefrigerating fluid in the support-distributor 21 have not been shown;they can have any appropriate configuration and distribution.

As a simple illustrative example, in a machine constructed according tothe invention, and having given complete satisfaction, thespecifications of the supportdistributor mentioned above were asfollows, for the production of a tube with an internal diameter, 4a, of15 I .Small plate 28 comprises, at theupstream end of its 2 mediangroove 29, a rounded edge not shown, facilitatits stability.

It will be noted that the weld unit-D of FIG. 1 comprisescomponentswithsimple shapes, easy to assemble and which are interchangeable. I 3

The operation of the device described and shown is as follows: thestarting strip of sheet metal 1, passes through theforming roller unitA, progressively taking up a more and more pronounced shaped in the formof a gutter, there being no danger of any folding or wrin kling, due tothe staggered position of the roller pairs. The horizontal rollers ofthe unit B then bring the edges of the strip of sheet metal alreadyshaped in the form of a gutter closer together and prepare its entryinto the conforming die unit C. In the latter unit, the conforming boot12, in cooperation with the plates 11, acts to form the lips 5 on theedges of the strip of sheet metal preparatory to feeding to the weldingbath, or it only completes said lips, if the latter have already beenpreformed on the edges of the strip by means, in particular, ofappropriately shaped roller pairs.

The two half-shells 20a, 20b in weld unit D, in cooperation withsupport-distributor 21, then provide a precise approach of the lipstoward each other, and the perfect alignment of said lips of the blankwith respect to the electrode of torch 4. The support-distributor 21also contributes to the guiding of the tube blank into the weld zoneand, because of its very special shape, it provides, in addition, for anoptimum distribution of the protective gas beneath the weld. ltalsoparticipates in providing efficient cooling of the welded tube, as doalso the half-shells 20a, 20b. i

The combination of all these means makes it possible to obtain a weldwhose quality is in no way inferior to that obtained by the meansdescribed in the previously mentioned prior application.

, The significance of the improvements obtained will appear clearly fromthe two following numericalcomparisons:

the cost of the welding unit constructed according to this invention isonly one tenth of that of the recip rocating welding unit providedaccording to the previous application;

the production, with an identical starting strip of sheet metal, hasbeen increased from 1.30 to 3m per minute.

It should be specified, finally, that the areas of application of thetwo machines under consideration are not identical. The device coveredby the previous application, operating step by step, is more appropriatefor the production of tubes with a diameter equal to or greater than 25mm, because of the very elaborate guiding and holding members which itcomprises. The one described and shown in the present application, whichis simpler and more rapid, is particularly suitable'for the, productionof tubes with a relatively small diameter.

Obviously numerous modifications of a constructive nature can beintroduced, .without departing from the scope of the invention,.into thevariousfcomponentsof the machinehere described and shown by simple wayof illustration.

I claim:

1. In a device for continuously producing smooth tubes having thin toextra-thin walls from a continuous strip of sheet metal of the typehaving a horizontally arranged series of roller pairs for forming thecontinuous strip first into a gutter and then into the outline of a tubewith a circular section open at its upper part, additional meansforforming an exterior oriented lip on each of edges at the upper part ofsaid tube blank and means for aligning and welding said lips, theimprovement comprising adjustable mounting'means fora plurality of saidpairs of forming rollers whereby the tube blank as it travels towardsaid welding means is made to travel along an upwardly sloping line tocompensate for the difference in length of travel between the edgeportions and the center portions of the strip, and means to introduceprotective gas to the interior of the tube adjacent the lips of the tubeblank in the region of the welding electrode.

2. The device as claimed in claim 1 wherein said roller pairs forforming the continuous strip include means for preforming the exteriororiented lips on the edge portions of the tube blank.

3. The device as calimed in claim 1 comprising tubular die meansdownstream of the pairs of forming rollers, and boot means down-streamof said die means for forming the lips on the edge portions of the tubeblank.

4. The device as claimed in claim 5 comprising tubular die meansdown-stream of the pairs of forming roll ers, and boot means down-streamof said die means for completing the formation of the lips initiated bysaid roller pairs.

5. The device as claimed in claim 4 wherein said lippreforming rollerpairs include a final pair of rollers having vertical axes.

6. A device for continuously producing smooth tubes having thin toextra-thin walls from a continuous strip of sheet metal, ofthe typehaving a horizontally arranged series of roller pairs for forming thecontinuous strip first into a gutter and then into the outline of a tubewith a circular section open at its upper part, comprising die meanswhich includes means for forming a pair of exterior lips oriented withrespect to each other on the respective edges of the tube blank, meansfor aligning said pair of lips and bringing them adjacent to oneanother, a stationary welding electrode adjacent said aligning means andpositioned to operate on said aligned lips, means for continuouslydrawing the tube blank through the aligning means and past saidstationary welding electrode, and means to introduce protective gas tothe interior of said tube adjacent said lips in the region of saidwelding electrode.

7. The device of claim 9, wherein said means for forming the pair ofexterior oriented lips comprises tubular die means down stream of theroller pairs for forming the tube blank and a boot means positioned downstream of said die means.

8. The device as claimed in claim 7 wherein said tubular die meanscomprises two portions separated along a diametrical horizontal plane,said boot means being attached to the upper portion of the tubular diemeans.

9. The device as claimed in claim 8 wherein the upper portion of saidtubular die means is shifted upstream with respect to the lower portionthereof whereby to extend the distance between said upper portion andthe welding electrode.

10. The device as claimed in claim 6, wherein the means for aligningsaid pair of lips comprises a pair of external half-shells surroundingthe tube and positioned below the welding electrode, each of saidhalfshells being mounted to freely pivot about a horizontal axis.

11. The device as claimed in claim 10, wherein said pivotally mountedhalf-shells are resiliently mounted on their horizontal axes to urge thesame together.

12. The device as claimed in claim 10 wherein said means for aligningsaid pairs of lips includes an upper plate, means for clamping saidplate onto the pair of half-shells, said plate containing a mediangroove for engaging the two lips of the tube blank, said plate endingadjacent to the welding electrode.

13. The device as claimed in claim l0wherein said half-shells containbores for the circulation of cooling fluid, means for feeding coolingfluid through said bores.

1. In a device for continuously producing smooth tubes having thin toextra-thin walls from a continuous strip of sheet metal of the typehaving a horizontally arranged series of roller pairs for forming thecontinuous strip first into a gutter and then into the outline of a tubewith a circular section open at its upper part, additional means forforming an exterior oriented lip on each of edges at the upper part ofsaid tube blank and means for aligning and welding said lips, theimprovement comprising adjustable mounting means for a plurality of saidpairs of forming rollers whereby the tube blank as it travels towardsaid welding means is made to travel along an upwardly sloping line tocompensate for the difference in length of travel between the edgeportions and the center portions of the strip, and means to introduceprotective gas to the interior of the tube adjacent the lips of the tubeblank in the region of the welding electrode.
 2. The device as claimedin claim 1 wherein said roller pairs for forming the continuous stripinclude means for preforming the exterior oriented lips on the edgeportions of the tube blank.
 3. The device as claimed in claim 1comprising tubular die means down-stream of the pairs of formingrollers, and boot means down-stream of said die means for forming thelips on the edge portions of the tube blank.
 4. The device as claimed inclaim 5 comprising tubular die means down-stream of the pairs of formingrollers, and boot means down-stream of said die means for completing theformation of the lips initiated by said roller pairs.
 5. The device asclaimed in claim 4 wherein said lip-preforming roller pairs include afinal pair of rollers having vertical axes.
 6. A device for continuouslyproducing smooth tubes having thin to extra-thin walls from a continuousstrip of sheet metal, of the type having a horizontally arranged seriesof roller pairs for forming the continuous strip first into a gutter andthen into the outline of a tube with a circular section open at itsupper part, comprising die means which includes means for forming a pairof exterior lips oriented with respect to each other on the respectiveedges of the tube blank, means for aligning said pair of lips andbringing them adjacent to one another, a stationary welding electrodeadjacent said aligning means and positioned to operate on said alignedlips, means for continuously drawing the tube blank through the aligningmeans and past said stationary welding electrode, and means to introduceprotective gas to the interior of said tube adjacent said lips in theregion of said welding electrode.
 7. The device of claim 9, wherein saidmeans for forming the pair of exterior oriented lips comprises tubulardie means down stream of the roller pairs for forming the tube blank anda boot means positioned down stream of said die means.
 8. The device asclaimed in claim 7 wherein said tubular die means comprises two portionsseparated along a diametrical horizontal plane, said boot means beingattached to the Upper portion of the tubular die means.
 9. The device asclaimed in claim 8 wherein the upper portion of said tubular die meansis shifted upstream with respect to the lower portion thereof whereby toextend the distance between said upper portion and the weldingelectrode.
 10. The device as claimed in claim 6, wherein the means foraligning said pair of lips comprises a pair of external half-shellssurrounding the tube and positioned below the welding electrode, each ofsaid half-shells being mounted to freely pivot about a horizontal axis.11. The device as claimed in claim 10, wherein said pivotally mountedhalf-shells are resiliently mounted on their horizontal axes to urge thesame together.
 12. The device as claimed in claim 10 wherein said meansfor aligning said pairs of lips includes an upper plate, means forclamping said plate onto the pair of half-shells, said plate containinga median groove for engaging the two lips of the tube blank, said plateending adjacent to the welding electrode.
 13. The device as claimed inclaim 10 wherein said half-shells contain bores for the circulation ofcooling fluid, means for feeding cooling fluid through said bores.